Sideband generator having step controlled modulation

ABSTRACT

A sideband generator, comprising a high frequency signal generator of frequency fo, a circuit for generating low frequency signals of frequency F0 1/T, characterized in that it comprises a bridge with two inputs and two outputs forming the sum and/or the difference of the signals fed to the inputs, the two inputs of said bridge being connected to the source of high frequency energy by means of numerically controlled distributing and phaseshifting means.

United States Patent [72] Inventor Michel Schilliger 31, rue des Oiscaux 91, Morangis, France [21] App1.No. 731,868 [22] Filed May 24, 1968 [45] Patented May 25, 1971 [32] Priority May 24, 1967 [33] France 31 107,704

[54] SIDEBAND GENERATOR HAVING STEP CONTROLLED MODULATION 9 Claims, 10 Drawm' g Figs. [52] 11.8. CI 332/47, 307/240, 307/269, 328/92, 332/43 [51] Int. Cl H031: H54 [50] Field of Search 332/43, 43 B, 47; 307/240, 269, 243, 321; 328/61, 63, 71, 72, 92, 97, 92(C.L.) [56] References Cited UNITED STATES PATENTS 2,377,858 6/1945 Bennett 332/43 B l 13,ss1,241

2,438,948 4/1948 Riesz 332/47 X 2,689,336 9/1954 McMillan 332/47 X 3,069,629 12/1962 Wolff 328/92 (C.L.)

3,135,874 6/1964 Lucas at al.. 328/97X 3,327,135 6/1967 Robb 332/47X 3,413,571 11/1968 Ulrick et al. 332/47X OTHER REFERENCES Eckhardt et al., Microwave-Carrier Modulation-Demodulation Amplifiers and Logic Circuits Feb. 1962 pp. 148 163 Proceedings of the IRE Primary Examiner-Alfred L. Brody Attorney-Craig, Antonelli, Stewart & I-Iill ZISETITIITBERATORS 2 1 S1 11 P2 1 13 14 15 16 17 18 CONSTVIggPFERS $8 TIMING GE RJEQQT OR Fig ,18' BISTABLE MULTI- VIBRATOR LOGIC CIRCUIT (HIGH FREQUENCY SIGNAL GENERATOR CONTROL ELEMENT FIG.] (PRIOR ART) 5-HIGH FREQUENCY SIGNAL GENERATOR F I (3.2 s 5'SET"|$ %RATQRS 12 21 1 4 i 20 13 14 1s 1s 17 18 1 SWITCH 1 JCONTROLLERS F I- hfif] 2 TIMING 9 m 118' *BISTABLE MULTI- VIBRATOR -nit LOGIC cmcun 1 LHIGH FREQUENCY SIGNAL GENERATOR CONTROL ELEMENT PATENTED HAYZSIQII 3.581.241

SHEET 3 BF 4 SIDEBANI) GENERATOR HAVING STEP CONTROLLED MODULATION This invention relates to a sideband generator and may be used to provide either two systems of sidebands by modulating a high-frequency signal to provide it with a stepped envelope at low-frequency in which each step lasts for the same time duration, or to provide an output carrier wave amplitude modulated by a periodic signal. More particularly the generator of the invention has the advantage that it is capable of being constructed to take advantage of integrated circuits with their attendant benefits.

In accordance with one aspect of the invention there is provided a sideband generator comprising a high-frequency signal generator producing a signal at frequency f,,, a circuit for generating lowfrequency signals at a frequency F,,=1/T, a bridge network having two input junctions and two output junctions from which are obtained the sum and/or the difference of the signals fed to the input junctions of the bridge which are connected to the high-frequency signal generator by a switchable phase-shifting means controlled by a numerically sensitive control element.

In accordance with a second aspect of the invention a sideband generator comprises a high-frequency signal generator producing a signal at frequency a low-frequency signal generating circuit producing asignal at a frequency F,,=l/T, a common path having a finite electrical length through which the high-frequency signals pass, switching means operating to alter, in equal steps, the electrical length of the path over a predetermined range of steps to provide at the output terminal of the line a high frequency signal whose amplitude varies in steps of equal time, diodes in said switching means having conducting and nonconducting states at which they respectively transmit and block the high-frequency signal to the line, and a numerically operated control element providing bias voltages applied to the diodes selectively to forwardly bias them to their conducting states when they are required to transmit the high-frequency signals and to back-bias them to their blocking states when they are not required to transmit the high frequency signals.

In the preferred application of the invention the highfrequency signal provides a carrier which is amplitude modulated by the low-frequency signal which is so applied that the modulation envelope appears stepped, each step lasting for the same time interval. In carrying out the invention use is preferably made of a hybrid bridge modulator composed of four sections of coaxial line arranged in the form of a bridge circuit and having one pair of opposite comer junctions providing input terminals and the other pair of opposite comer junctions providing output terminals. Three of the arms have a length AM, where A is the wave length of the high frequency signal, while the remaining arm has a length of 3. k/4. If the output cornerjunctions are suitably provided with impedances matching the line impedance of the coaxial an'ns of the bridge, advantage can be taken of the well-known properties of quarter-length line transformers to provide at the output comer junctions of the bridge the high-frequency signal whose amplitude fluctuates in accordance with the path length extending from the high-frequency signal generator to the output comer junctions of the bridge.

In carrying out the invention with a coaxial bridge network, the input corner junctions of the bridge are preferably con nected to receive the high frequency signal from a switching circuit which injects the high-frequency signal at predetermined points spaced from the electrical center of the connection extending between the two input corner junctions of the bridge. The switching circuit may be arranged to step between predetermined intennediate positions at equal intervals of time, each position introducing a small difference in the path length extending from the high frequency generator to each of the two output corner junctions of the bridge. The phase suppression properties of the bridge can be arranged to produce a reduction in the amplitude of the high-frequency signal fed to one output corner junction while simultaneously an increase in the amplitude of the high-frequency signal fed to the opposite cornerjunction.

The invention will now be described. in more detail, by way of examples, with reference to the accompanying drawings, in which:

FIG. I illustrates a coaxial line bridge network of known yp FIG. 2 is a block schematic diagram of a sideband generator;

FIGS. 3, 4 and 5 illustrate signals appearing at various points in the circuit of FIG. 2 over a period of time T which is equal to the inverse of the desired frequency of modulation;

FIGS. 6, 7, 8 and 10 show switching and control circuits shown in block form in FIG. 2; and,

FIG. 9 shows a logic circuit represented in block schematic form in FIG. 2.

Turning first to FIG. 1 this shows a coaxial bridge circuit of known type having four coaxial lines I, 2, 3 and 4 each of 50 ohms impedance and connected at comer junctions A, B, C and D. The coaxial lines I, 2 and 3 are each of length equal to M4 (where )t is the wavelength of a high-frequency input signal at a frequencyf while line 4 has a physical length 3M4. A fifth line 6 also of 50 ohms impedance interconnects the input cornerjunctions A and B of the bridge network and the center M of line 6 is connected to a high-frequency signal generator 5 producing a continuous carrier frequency signal f,,. The electrical length of the fifth line extending from M to A is equal to the electrical length of the portion of the line extending from M to B and introduces into the signal fed from the high frequency generator 5 at phase shift I The two output comer junctions C and D are earthed respectively through a pair of SO-ohm impedances 7 and 8 which match the coaxial line impedance of the bridge.

In the bridge of FIG. 1 the voltages at the corner junctions A and B are equal as the phase shift of the input signal f applied to them is the same, the path length MA and MB being equal.

Considering first electrical energy introduced into the bridge at corner junction A, the two path lengths ACE and ADB, being of half a wavelength difference, result in corner junction B appearing, when viewed from corner junction A, as a short circuit. Likewise, corner junction A appears, when viewed from corner junction B, also as a short circuit. Considering now the output corner junction C, this will receive energy from input cornerjunctions A .and B. However, as the length of the line 4 is half a wavelength different from the length of the line I, the voltage at C will always be zero as the signals received from corner junctions A and B are in an tiphase with one another. As corner junction C is terminated with a matching impedance there is no reflection of energy back into the bridge.

Turning now to corner junction D, this receives energy from comer junctions A and B which, as the path lengths of the coaxial lines 2 and 3 are the same, will always be in phase. All of the energy directed into the bridge is therefore extracted at the corner junction D which is terminated with 50 ohms matching impedance to prevent back reflection of energy into the bridge.

It follows from the analysis of the functioning of the bridge network that the voltages at the corner junctions A and B are made different by positioning the input contact on line 6 an electrical distance from point M. However, all of the power fed into the bridge will still be distributed between the output comer junctions C and D but the relative strengths of the output signals at these corner junctions will be a function of the displacement from point M of the position of introduction of the highfrequency signals from the generator 5.

FIG. 2 illustrates a circuit diagram of a sideband generator which takes advantage of this feature and produces a lowfrequency modulation envelope of 30 c/s and of stepped configuration providing for each quarter period eight steps equispaced in time as shown in FIG. 3. In the block circuit diagram of FIG. 2 the numerals 1 to 6 refer to the same components as are correspondingly numbered in FIG. I. It will be seen that the fifth line 6 in FIG. 2 is equipped with several contacts E, to E located on the same side of the center point M of the line, the electrical path lengths MA and MB being equal. To simplify the drawing only E, and E are referenced and they are represented as contact studs of a switching circuit X having a switch arm 10 which is connected at point G to an input signal generator 5. Generator delivers a high-frequency continuous signal atf =l l0 Mc/s.

Operation of the switching circuit X is accompanied by stepping of the switch arm between the studs E, to E The stepping movement is controlled by a control element 11 which has eight inputs respectively to eight output control terminals n,n of a logic circuit 12. In actual practice the operation of the switching circuit X is controlled electronically by the control element 11 as is explained in more detail below with reference to later Figures which have still to be described.

A timing signal generator 13 supplies a signal at 960 c/s which operates a counter having five binary stages. The first four binary stages are formed by bistable multivibrators 14, l5, l6 and 17 which are mounted in series and each of which provides a pair of complementary outputs. The fifth stage of the counter is formed by two bistable multivibrators 18 and 18' which are connected to receive respective outputs of the complementary pair of outputs from the multivibrator 17. Each of the two multivibrators l8, 18' gives a pair of complementary outputs which are individually fed to input control terminals m to m,, of the logic circuit 12. The eight outputs from the four multivibrators 14 to 17 are respectively connected to input control terminals m, to m of the logic circuit 12.

The output comer junctions D, C of the bridge network are respectively connected to contact pairs p,, p and q,, q The contacts p, and p are connected by a coaxial line 19 which introduces a phase displacement of half a wavelength. Likewise a coaxial line 22 introduces a phase displacement of half a wavelength. Likewise a coaxial line 22 introduces a displacement of half a wavelength between the contact pair q, and q Associated with the two contact pairs are respective switching members 20, 23 which are controlled by switch controllers 21 and 24. The switch controller 21 receives two inputs from the output control terminals n and H of the logic circuit 12 and controls operation of the switching member 20, while the switch controller 24 receives two inputs from the output control terminals n and n and controls operation of the switching member 23. When the switching members and 23 are in respective positions p and q the high-frequency signal delivered at main output terminals S, and S suffers a phase inversion as a result of the half wave lines 19 and 22.

The circuit diagram of FIG. 2 operates as follows.

Assuming firstly that the control element 11 has positioned switch arm 10 at position E,. The high frequency signal supplied by the generator 5 is transmitted through the switch arm and the contact E, to the input corner junctions A and B of the bridge network by way of the paths E,A and E,B. The voltages at input comer junctions A and B are given respectively by the formulas:

In these formulas Vsinmt is the input voltage received at point G; 1 is the phase shift introduced by the lengths of the paths MA or MB and III is the phase shift introduced by the line length ME,. The bridge network lines AC and BC are transformers with a transformation ratio of 1H2 and introduce phase shifts of 1r/2 and 31r/2 respectively. In consequence the highfrequency voltage at the comer junction C is:

As the coaxial lines AD and BD are each quarterwavelength transformers of ratio i i 2, the high frequency voltage at cornerjunction D is given by the equation:

The switch arm 10 is switched in turn to each of the intermediate contacts E,E during successive equal periods of AT=l/960 second. The switch arm 10 spends a time of 2AT on the contact E for the reason seen immediately in FIG. 3 and it then steps back over the intermediate contacts during successive periods of time AT until it reaches E, at which it is again held for a period 2AT. The distance between E, and E approximates to a quarter-wavelength so as to obtain at the corner junctions C and D high-frequency signals which are in phase with one another but whose levels vary as the sine and cosine of the electrical angle.

The logic circuit 12 is controlled by the timing signal generator 13 supplying signals at a frequency of 960 c/s to the binary counter whose five binary stages with double complementary output transform the high-frequency signal f from generator 5 into two systems of sidebands contained in a modulation envelope of 30 CIS and shifted in phase by with respect to one another.

FIGS. 3 and 4 represent respectively the two 30 c/s sideband systems. The sideband level is denoted by the axis y, in FIG. 3, and by the axis y in FIG. 4. The 30 cycle modulating envelope is of stepped form and is divided into equal time intervals corresponding to each step in dependence upon the signals appearing at the output control terminals n, to n, of the logic circuit 12. In FIG. 5 these signals bear the reference (n,) to (u and they control the stepping of the switch arm 10 of the switching circuit X between the positions E, to E They also control by way of the output control terminals n,, to n, the operation of the switching members 20 and 23 which determine whether the phase inverting lines 19, 22 are introduced between the output of the bridge network and respective main output terminals S, and S The switch arm 10 is in the position E, for a time AT=1/96O second during which time the high-frequency signal from the generator 5 is applied to the bridge. During the first quarterperiod of the 30 cycle modulating signal, that is to say until time T/4 where T=l/30, the two switching members 20 and 23 are in respective positions p, and q, as is dictated by the signals (n,,) and (n delivered to the output control terminals n,, and n of the logic circuit 12. The phase inversion of the signal at the main output terminal S, is produced by the insertion of the coaxial line 19 between the output corner junction C and the mainoutput terminal 8,. This is done in response to the signal (n, from terminal such signal being fed to the switch controller 21 when the switch arm 10 is in position E,. Likewise the inversion of the signal at the main output terminal S by inserting the coaxial line 22 between the output corner junction D and the main output terminal S is brought about by the signal (n fed to the switch controller 24 from the output control terminal n when the switch arm 10 is in the position E The two coaxial lines 19 and 22 are isolated when the signals (n,,) and (n appear respectively at the output terminals n,, and n,.

It will be noted that the above-described circuit could be used to provide an amplitude modulator. In fact, if the output signal at the corner junction D of the bridge network is connected directly to main output terminal S which is terminated with a SO-ohm impedance to match the coaxial line impedance of the bridge, there is obtained on the other main output terminal S, which is directly connected to the output comer junction C of the bridge, an amplitude modulated wave. Such a modulator does not require the presence of the phase inverting lines 19 and 22 of length M2, or the switch controllers 21 and 24 and their instructing multivibrators I8 and 18 which form the last stage of the binary counter and take care of the signal phase inversion. In such an amplitude modulator, the respective positions of the contacts E, to E on the fifth line 6 will be suitably selected to provide the shape of modulating waveform required.

It should also be noted that the contacts E,E,, can be arranged in such a manner as to make possible the application of phase shifts varying in inverse direction and by discrete jumps from to 21r in a time T and to obtain the modulation sidebands directly at C and D without requiring the phase inverting lines 19 and 22 together with their associated switch controllers and switching members.

FIG. 6 shows electronic circuitry which may be used as the switching circuit X of FIG. 2 in order to switch the highfrequency signal fl, from the generator between the contacts E, to E of the fifth line 6. The circuit of FIG. 6 responds only to the presence of the output signal at the output control terminal n, of the logic circuit 12 in order to establish a connection between the highfrequency generator.5 and the fifth line 6, and it will be understood that similar circuits take care of the switching of the connections to the other contact E, in response to other signals appearing at different output control terminals n to u The output control terminal n, of logic circuit 12 is connected through a resistance 25 to the base of an NPN transistor 26 having its emitter connected to a terminal 33 held at a negative voltage and its collector connected through a pair of resistors 27 and 28 to a terminal 34 held at a high positive voltage. The junction of the resistances 27 and 28 is connected through an inductance 29 to a junction formed between a capacitor 31 and a cathode of a diode 30. The anode of the diode is connected to contact E, of the coaxial line 6 which feeds the input corner junctions A and B of the bridge. A point K of the portion of the line 6 extending between contact E and comer junction B is earthed through a high value inductance 35. The capacitor 3! is connected through a coaxial line 32 of length M2 to an output point G of the high-frequency generator 5 which delivers signal f,,.

The transistor 26 is switched into its conductive condition by the presence of a signal at the output terminal n, of the logic circuit 12. A' negative voltage appears at the common point of the diode 30 and the capacitor 31 when this occurs, and forwardly biases the diode 30 which therefore conducts allowing the high-frequency signal f supplied by the generator to be transmitted through the diode to the terminal 13,.

In the absence of the signal at the output control terminal n,, the transistor 26 does not conduct and a positive voltage appears at the common point between the diode 30 and the capacitor 3H. This voltage is positive with respect to earth so that the diode 30 is back-biased into its nonconducting condition and therefore prevents the transmission of the highfrequency signal to the contact E,.

The above described circuit is duplicated for each of the connections between the output control terminals n, to n,; and the contacts E, to E The generator 5 is connected in common at G to the extremities of all of the coaxial lines such as 32 associated with the switching circuit. During normal functioning only one of the diodes 30 is conducting at any time interval AT. The diodes 30 are preferably selected to have a high conductance to reduce losses when in their conducting condition, and a low capacitance so that there is no risk of perturbations being introduced into the bridge network as a result of the comer junction B having a very large impedance attached to it when the diode 30 is not conducting.

FIGS. 7 and 8 illustrate alternative switch control circuits which may be used to introduce the half-wavelength lines 19 and 22 in the circuitry extending from the bridge network to the main output terminals S, and 5,.

In FIG. 7 the output comer junction C of the coaxial line bridge of FIG. 2 is connected to the main output terminal S, through a rectifying bridge composed of four diodes 36, 37, 38 and 39 and a coaxial line 40 of length M2 connected between the cathodes of the diodes 37 and 38.

The output control terminals n, and n,, of the logic circuit 12 of FIG. 2 are connected, in FIG. 7, to respective bases of a pair of NPN transistors 41 and 42. The transistor emitters are respectively connected to a terminal 47 held at a constant negative voltage and the transistor collectors are respectively connected through two resistance chains 4344 and 4546 to a terminal 48 held at a positive high voltage with respect to earth. The junction of the resistance 43 and 44 is connected through and inductance 49 to the cathodes of the bridge diodes 36 and 39, and the common junction of the other resistance chain 45, 46 is connected through a second inductance 50 to the junction of the coaxial line 40 with the cathode of bridge diode 38. The anodes of the four bridge diodes are earthed through inductances 51 and 52 of high value.

The transistors 41 and 42 are controlled by the signals appearing simultaneously on the output control terminals n,, and n of the logic circuit 12 insuch a way that one of them is always in its conducting condition when the other is blocked, that is to say nonconducting. For example, if the transistor 41 is conducting, the diodes 36 and 39 are biased into their conducting conditions and therefore have flowing through them a continuous current which enables them to transmit the highfrequency signal supplied at the output comer junction C of the bridge network (not shown) to the main output terminal 8,. If now the transistor 42 conducts and the transistor 41 is nonconducting or blocked, the other pair of diodes 37 and 38 conduct and allow the high-frequency signals from the output corner junction C of the bridge rectifier to be transmitted by way of the half-wavelength line 40 to the main output terminal 5,. This results in a phase inversion of the signal at the main output terminal 8,.

FIG. 8 illustrates an alternative phase shifting circuit which may be connected between the output corner junction C of the bridge network and the main output terminal 8,. The circuit of FIG. 8 is controlled by the signals appearing at the output control terminals n,, and n, of the logic circuit 12 as formerly described with reference to FIG. 7. The output corner junction C of the bridge is connected. to the main output terminal S, through a first diode 53 having its cathode connected through a capacitor to the main output terminal, and through a second diode 54 whose cathode is connected through a capacitor and a half-wavelength line 57 to the main output terminal S,. The diodes 53 and 54 have their cathodes respectively connected through two inductances 55 and 56 to intermediate points in a pair of resistance chains provided between the collectors of two NPN transistors 58, 59 and a source of positive voltage. The bases of the transistors 58, 59 are respectively connected to the output control terminals n n, of the logic circuit 12 and the transistor emitters are connected to a common source of negative voltage.

The presence of a signal on the terminal n,, occurs when there is no signal on the output control terminal 11, so that the transistors 58, 59 are selectively conductive. The circuit is so arranged that the diode 53 is forwardly biased into the conducting condition by the signal (n,,) while the diode 54 is blocked through being. back-biased. The signal from the output corner junction C of the bridge network is now transmitted to the main output terminal S, by way of the diode 53. If now the diode biasing is reversed so that the diode 54 becomes conductive and the diode 53 is blocked, the signal supplied at the output corner junction of the bridge passes through the line 57 which introduces into it a phase shift of 11-.

FIG. 9 illustrates the logic circuit 12 which supplies control pulses to the control element 11 and to the switch controllers 21 and 24 of FIG. 2.

Referring to FIG. 9 the input control terminals m,m,, are connected to the complementary pairs of outputs of the multivibrators 14ll7 of FIG. 2, and the terminals m,,-m are connected individually to the complementary outputs of the multivibrators l8 and 18'. The circuit for switching the high frequency signal f from the generator 5 to the selected contact E,E,, is similar to that shown in FIG. 6, the diode 30 being conductive or not according to the state of the multivibrators M17. It can be easily shown that the signal (n for producing an output at the outptg go ntrol terminal n, is:

(n )=a.b.c..+a.b.c..

In this equation a and a, b and b, c and c, d and d are the complementary signals delivered respectively at the outputs of the multivibrators M to 17 and applied to the inputs m,m

Turning to FIG. 9 the signals a, a.....d, d are transmitted to the output control terminal n in accordance with the signal (n,) by means of: a first group of AND gates which includes the AND gate 60 having two inputs, for example connected to m and m a second group of AND gates such as the AND gate 61 having two inputs respectively connected to two outputs of two AND gates such as 60; and a third group of OR gates such as the OR gate 62 having two inputs respectively connected to two outputs of two of the AND gates 61. The output of each OR gate such as 62 is connected to one of the output control terminals n,-n

The four outputs of the multivibrators 18' and 18 are connected respectively to the input control terminals In -m which are directly connected to the output control terminals n,,n of the logic circuit 12. The signals delivered at the output control terminals n,-n, are illustrated in F IG. 5.

FIG. 10 illustrates an embodiment of the line 6 shown in FIG. 2, with multiple contacts E,E connected in succession by diode circuits to the point G of the output of the generator 5.

The line is constituted by a flat metal strip 65 located between two metal plates, of which only one, 66 is shown, so as to obtain an impedance of 50 50-ohrns. The metal strip is looped back and forth several times so as to provide loops such as loop 67, having at their inner ends the contacts E E in such an arrangement, the physical distance between the input point G for the frequency f,,, and the contacts E,-E. is small, and the impedance provided at G by the blocked diodes, such as 30, is very high.

The line 6 may thus comprise simply a flat metal box with three coaxial terminals M, B and G and eight contacts for controlling the biasing of the diodes 30 in a similar manner as described above with reference to FIG. 6.

A sideband generator as described above is capable of dividing the power of an input signal with phase inversion, and may be used to. feed two transmitter aerials with a set of side bands to provide an omnidirection radio beacon operating at very high frequency (V.H.F. (VOR)). ln fact, at the main output terminal 8,, the signals delivered vary in amplitude and phase as the sine of an angle, passing through maximums of 90 and 270 and minumum values with phase inversion of to 180, whereas the signals supplied at the main output terminal vary as the cosine of the same angle passing through maximum values of 0 and 180 and through minimum values with phase inversion at 90 and 270.

The example of sideband generator described in the foregoing can also be employed in particular for generating on a single output sidebands of modulation of 90 CIS and 150 c/s which may be usefully employed in particular in instrument landing systems (l.L.S.), these examples not being in any way intended to be restrictive.

What we claim is:

l. A sideband generator, comprising a high-frequency signal generator of frequency f}, a circuit for generating lowfrequency signals of frequency F,,=l/T, where T is the period of a low-frequency signals F characterized in that it comprises a bridge with two input and two outputs forming the sum and/or the difference of the signals fed to the inputs, the two inputs of said bridge being connected to the source of high-frequency energy by means of a switchable phase-shifting means controlled by a numerically sensitive control element, connected to said circuit for generating low-frequency signals, for controlling the amplitude of the high-frequency signals fed to said bridge and further characterized in that the circuit connecting the two inputs of said bridge comprises an electric line fitted with a plurality of input contacts for the high-frequency signal and a numerically controlled switching circuit which switches the output of the said line, to provide at the two inputs of said bridge high-frequency signals .whose phase shifts vary simultaneously in inverse direction and by discrete jumps, and I wherein said switching circuit of the high-frequency generator comprises a plurality of diodes, each having a first electrode connected to one of the aforesaid input contacts and a second electrode connected, on one hand, to the output of said high-frequency signal generator and, on the other hand, to one of the outputs of the associated control circuit whose inputs are connected to the outputs of a counter with bistable multivibrators of a circuit of the low-frequency signal generator, to render said diodes conducting in succession for the high-frequency signal.

2. A generator according to claim 1, characterized in that said aforementioned electric line is provided with n input contacts arranged on one side of an electric center point of said line and the electrical distance between said electric center point in any one of the n contacts is between 0 and A/4'at frequency f, for producing at the outputs of the aforesaid bridge squared side bands of modulation with n levels equitime divided during a time T/4.

3. A generator according to claim 2, characterized in that it comprises two numerically controlled phase-inverter circuits, connected respectively to the two outputs of said bridge in order to apply in succession a phase shift of value 1r and a phase shift of value 0 respectively during time intervals equaling T/2 to the squared signals supplied at the two outputs of said bridge.

4. A generator according to claim 3, characterized in that each numerically controlled phase-inverting circuit comprises a transmission line of length M2 at frequency f,,, as well as control means associated with said transmission line for connecting said line in series or in short-circuit with one of the outputs of aforesaid bridge.

5. A generator according to claim 4, characterized in that the means for controlling the phase inversion associated with each inverter comprises two transistors, two first electrodes of which are connected respectively to two outputs of the lowfrequency signal generating circuit, and two second electrodes of which form two outputs respectively connected to two inputs of the aforesaid phase inverter.

6. A generator according to claim 5, characterized in that each phase inverter circuit comprises a four-arm network, three first arms of which each comprise a diode and the fourth includes a diode in series with the transmission line, a first corner of which between two diodes of one of said first three arms and the fourth arm is connected to one of the outputs of said bridge, while two other corners comprised between two diodes and adjacent to said first corner are connected to the two outputs of said associated phase-inversion controlling circuit.

7. A generator according to claim 5, characterized in that each phase-inverter circuit comprises two diodes two identically polarized electrodes of which are connected in common to one of the outputs of said bridge and the two electrodes of which are respectively connected, on one hand, to the two extremities of said transmission line and, on the other hand, to the two outputs of the associated phase-inversion controlling circuit.

8. A generator according to claim 2, characterized in that the aforesaid electrical line is constituted by a folded-back metal strip, so as to form n-l loops and provided with the aforementioned n input contacts connected respectively by switching circuits with diodes to a central point connected to the output of said generator of the high-frequency signal, the respective distances from said center point to the said it input contacts being small order that the impedance provided by a diode at the center point be very large.

9. A sideband generator according to claim 1, comprising a high-frequency signal generator of frequency f,,, a circuit for generating low-frequency signals of frequency F,,=l/ T, where T is the period of a low-frequency signal F characterized in tacts for receiving signals generated by said high-frequency signal generator, means by switching the output of said highfrequency signal generator to the input contact of said line, including a plurality of diodes connected between said input contacts and said high-frequency signal generator and a circuit controlled by said low-frequency signal generator, and a means controlling the period of conduction of said diodes, for varying the electrical path length of said line, to thereby provide a phase shift in portions of said electric line in discrete steps. 

1. A sideband generator, comprising a high-frequency signal generator of frequency Fo, a circuit for generating low-frequency signals of frequency Fo 1/T, where T is the period of a lowfrequency signals Fo, characterized in that it comprises a bridge with two input and two outputs forming the sum and/or the difference of the signals fed to the inputs, the two inputs of said bridge being connected to the source of high-frequency energy by means of a switchable phase-shifting means controlled by a numerically sensitive control element, connected to said circuit for generating low-frequency signals, for controlling the amplitude of the high-frequency signals fed to said bridge and further characterized in that the circuit connecting the two inputs of said bridge comprises an electric line fitted with a plurality of input contacts for the high-frequency signal and a numerically controlled switching circuit which switches the output of the said line, to provide at the two inputs of said bridge high-frequency signals whose phase shifts vary simultaneously in inverse direction and by discrete jumps, and wherein said switching circuit of the high-frequency generator comprises a plurality of diodes, each having a first electrode connected to one of the aforesaid input contacts and a second electrode connected, on one hand, to the output of said highfrequency signal generator and, on the other hand, to one of the outputs of the associated control circuit whose inputs are connected to the outputs of a counter with bistable multivibrators of a circuit of the low-frequency signal generator, to render said diodes conducting in succession for the high-frequency signal.
 2. A generator according to claim 1, characterized in that said aforementioned electric line is provided with n input contacts arranged on one side of an electric center point of said line and the electrical distance between said electric center point in any one of the n contacts is between 0 and lambda /4 at frequency fo for producing at the outputs of the aforesaid bridge squared side bands of modulation with n levels equitime divided during a time T/4.
 3. A generator according to claim 2, characterized in that it comprises two numerically controlled phase-inverter circuits, connected respectively to the two outputs of said bridge in order to apply in succession a phase shift of value pi and a phase shift of value 0 respectively during time intervals equaling T/2 to the squared signals supplied at the two outputs of said bridge.
 4. A generator according to claim 3, characterized in that each numerically controlled phase-inverting circuit comprises a transmission line of length lambda /2 at frequency fo, as well as control means associated with said transmission line for connecting said line in series or in short-circuit with one of the outputs of aforesaid bridge.
 5. A generator according to claim 4, characterized in that the means for controlling the phase inversion associated with each inverter comprises two transistors, two first electrodes of which are connected respectively to two outputs of the low-frequency signal generating circuit, and two second electrodes of which form two outputs respectively connected to two inputs of the aforesaid phase inverter.
 6. A generator according to claim 5, characterized in that each phase inverter circuit comprises a four-arm network, three first arms of which each comprise a diode and the fourth includes a diode in series with the transmission line, a first corner of which between two diodes of one of said first three arms and the fourth arm is connected to one of the outputs of said bridge, while two other corners comprised between two diodes and adjacent to said first corner are connected to the two outputs of said associated phase-inversion controlling circuit.
 7. A generator according to claim 5, characterized in that each phase-inverter circuit comprises two diodes two identically polarized Electrodes of which are connected in common to one of the outputs of said bridge and the two electrodes of which are respectively connected, on one hand, to the two extremities of said transmission line and, on the other hand, to the two outputs of the associated phase-inversion controlling circuit.
 8. A generator according to claim 2, characterized in that the aforesaid electrical line is constituted by a folded-back metal strip, so as to form n-1 loops and provided with the aforementioned n input contacts connected respectively by switching circuits with diodes to a central point connected to the output of said generator of the high-frequency signal, the respective distances from said center point to the said n input contacts being small order that the impedance provided by a diode at the center point be very large.
 9. A sideband generator according to claim 1, comprising a high-frequency signal generator of frequency fo, a circuit for generating low-frequency signals of frequency Fo 1/T, where T is the period of a low-frequency signal Fo, characterized in that it comprises a bridge with two inputs and two outputs forming the sum and/or the difference of the signals fed to the inputs, the two inputs of said bridge being connected to the source of high-frequency energy by means of a switchable phase-shifting means controlled by a numerically sensitive control element, connected to said circuit for generating low-frequency signals, for controlling the amplitude of the high-frequency signals fed to said bridge and further characterized in that the circuit connecting the two inputs of said bridge comprises an electric line fitted with a plurality of input contacts for receiving signals generated by said high-frequency signal generator, means by switching the output of said high-frequency signal generator to the input contact of said line, including a plurality of diodes connected between said input contacts and said high-frequency signal generator and a circuit controlled by said low-frequency signal generator, and a means controlling the period of conduction of said diodes, for varying the electrical path length of said line, to thereby provide a phase shift in portions of said electric line in discrete steps. 